In an electric discharge machine, when machining is conducted on a workpiece by an electrode in a machining solution filled in a machining tank, a temperature of the machining solution is changed by a change in the peripheral temperature and a rise in the temperature of the electric discharge machine body in the process of electric discharge machining. As a result, a relative position between the electrode and the workpiece is changed, and the machining accuracy is lowered. In order to solve the above problems, it is common to use a temperature control unit for conducting ON/OFF control of electric power so that the temperature of the machining solution can be controlled to a value close to a predetermined reference temperature (target temperature).
However, the above temperature control unit is controlled in such a manner that when the temperature of the machining solution is increased higher than the target temperature, electric power is turned on and the blowing of air is started so as to lower the temperature of the machining solution and when the temperature of the machining solution is decreased lower than the target temperature, electric power is turned off and the blowing of air is stopped so as to raise the temperature of the machining solution. Accordingly, the temperature of the machining solution fluctuates round the target temperature. Therefore, the smaller the capacity of the temperature control unit, the larger the thermal displacement of the electric discharge machine body due to a change in the temperature of the machining solution. As a result, the machining accuracy is deteriorated. Even when the capacity of the temperature control unit is increased, the temperature of the machining solution is changed. Therefore, the thermal displacement is caused in the electric discharge machine body, and the cost is increased.
Recently, there has been an increasing requirement of enhancing the machining accuracy of electric discharge machining. In order to meet the requirement, it is necessary to suppress the deterioration of the machining accuracy caused by a change in the temperature of the machining solution.